Even in the antibiotic era, S. aureus remains one of the most feared pathogens with a spectrum of disease ranging from local abscesses to overwhelming sepsis. One of the unique features of S. aureus is its ability to cause metastatic infections. The factors that permit the development of these metastases are not known. We have found that fibronectin binds to S. aureus avidly and specifically and that the number of fibronectin receptors on the strain of S. aureus correlates directly with its invasiveness. Fibronectin is found in abundance at sites of endovascular damage and may serve as an attachment site for S. aureus. Thus, the overall goal of this grant is to characterize the role of fibronectin in the pathogenesis of endovascular, S. aureus infections. We plan to characterize the fibronectin binding factor on S. aureus, to produce antibodies against the fibronectin binding substance on S. aureus, to study the role of fibronectin in the adherence of S. aureus to host tissues in animals using in vitro models of endovascular infection, and to characterize the effects of fibronectin on phagocytosis by endothelial cells and fibroblasts. Because S. aureus infections represent a common and serious threat to patients with artificial or abnormal heart valves; a better understanding of the initiating event, i.e., attachment to tissues, will help to design more rational therapy. The importance of fibronectin in pathogenesis of S. aureus infections will be determined by using fibronectin fragments and antifibronectin antibodies. If S. aureus attachment to fibronectin proves important in the initiation of S. aureus infections, then antibodies directed at the fibronectin receptor on S. aureus may be able to prevent these infections. This suggests the possibility of a vaccine. We plan to isolate the fibronectin receptor on S. aureus by fibronectin-Sepharose affinity, by QAE, and gel-filtration chromatography. We will study attachment of S. aureus in vitro by testing adherence of S. aureus to clots, subendothelial matrices, collagen-fibronectin matrices, endothelial cells, and fibroblasts. Use of fibronectin fragments and antibodies to the fibronectin receptor will provide specificity for the S. aureus-fibronectin interactions. Finally, ultrastructural and histochemical studies of S. aureus interactions with fibronectin and host cells will be performed.